From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id CF426C982DA for ; Fri, 18 Sep 2026 12:18:23 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id E1CAF6B0093; Fri, 18 Sep 2026 08:18:22 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id DED916B0096; Fri, 18 Sep 2026 08:18:22 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D02D96B0098; Fri, 18 Sep 2026 08:18:22 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 9DE506B0093 for ; Fri, 18 Sep 2026 08:18:22 -0400 (EDT) Received: from smtpin09.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 155721A0624 for ; Fri, 18 Sep 2026 12:18:22 +0000 (UTC) X-FDA: 85226785644.09.DAFFAFD Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf31.hostedemail.com (Postfix) with ESMTP id 5D76720002 for ; Fri, 18 Sep 2026 12:18:20 +0000 (UTC) Authentication-Results: imf31.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=nHi3LIql; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf31.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1789733900; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=iraf2G8GnLk55v/tOz9PuW5FKw3tZzsJG7inOso05Qw=; b=LLIBSJhA9MjF1XtdAUGhdBnZYHr1wIk6+xgrDDfdeaztkyPRJmNM7Yv6G7a4K9y8dB/tEC hvJmAAuPrDnfzLCVQUtTpynhRo3RenjhzdC+8+xJGGbgKtK8/56a0yvKRHbSBXWIlA6Lum KzaX+NtaP5rhhbPYJySoz3zPGmgH2Jg= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1789733900; b=uqU2lXdB5jy+Eh1mjD2FDsl9u2qc6qw63NN5TOGwUrwixogO448L00UDt8aY+/VmluWskX wu7PvTW0yqm5WKpN0+b/YWUXcmV2hmlrOcn94Zx4So/9bWAP++frqzn9fHvNQwldP3Mewb /hDr7IXH551jT0tg8Y2xEn1OcAmO6jk= ARC-Authentication-Results: i=1; imf31.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=nHi3LIql; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf31.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id A88A660A89; Fri, 18 Sep 2026 12:18:19 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 251121F000FF; Fri, 18 Sep 2026 12:18:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789733899; bh=iraf2G8GnLk55v/tOz9PuW5FKw3tZzsJG7inOso05Qw=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=nHi3LIqlfCjI2cn+NwQvM+CZ6Xylz1qzVBvMVHU9ino6iJj0S1Gv6y6qT3JyuiqVw 9NwLROYnHXnhBnwRDXtkpuBo0RiuhYfP372H/PrZ5Nmt5H7qMGr4ZvjDP7Dwj0hTX6 t9ukArpPNzDq/p+rmRjeDwz2aikNKZW1dqPzMlSgMIrL0+8GchhWkMtqhxcMBbwlYM HZJToJz+7PH7D09H/haTWnVS9i0c84gZW++nFFnRWSopuUlryKmKqMgcjwZv21FwQz Y2Neq90H9WGRd9haugFuPUNOpXZWqNTYrEEcEwM034L57yQl4mqvl9boN1WzzbFTxb aVrL4ESb4oOWg== Message-ID: Date: Fri, 18 Sep 2026 14:18:03 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 7/9] drivers/base/memory: count inherited poisoned frames into the block To: Breno Leitao Cc: Ard Biesheuvel , Ilias Apalodimas , Miaohe Lin , Naoya Horiguchi , Andrew Morton , kas@kernel.org, kexec@lists.infradead.org, Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Brendan Jackman , Johannes Weiner , Zi Yan , Oscar Salvador , Greg Kroah-Hartman , "Rafael J. Wysocki" , Danilo Krummrich , hannes@cmpxchg.or, shakeel.butt@linux.dev, linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, rmikey@meta.com, riel@surriel.com, harry@kernel.org, linux-cxl@vger.kernel.org, driver-core@lists.linux.dev, kernel-team@meta.com References: <20260915-hwpoison-kho-v5-0-3bc7a57bd503@debian.org> <20260915-hwpoison-kho-v5-7-3bc7a57bd503@debian.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 5D76720002 X-Stat-Signature: fm4oki77eezj3o8bfofrpogymbkxegkb X-HE-Tag: 1789733900-201048 X-HE-Meta: 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 gpoQT/fk QHwXh/ct8jXiqifpRsmXj9P4VCOOxzZEECVz977UyJiJo/Z3rwM1jHoyXOAwTkn2JMSCxta3yE6FVi++Fzz5KNnuH6uNckMxbp6BLuVmcdwbS47IlowDoYt1dyRcqHze9X/K+bnaW24uEB35d8nTMH632Q9fAl+rWMspysX+aZlQ///9p+oJ1miGvfyy/8ScATU10sxyC/0v29dJPLTpzdGV3UWH4kSyNpzKX4QWYJyoR8/Lp0FATteHVmYQYZ+OBx7Xuw17zskQn5k2SXIL4+E20gB5a5ETkV5xADbremiRLBKj54JmBbjsGtv2k+k6IP7XLsJlm+BUhe0qyUmWUM1zK0Z2B84mz5Hkw3Rff5kyJsLQ= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/17/26 15:01, Breno Leitao wrote: > On Wed, Sep 16, 2026 at 04:51:40PM +0200, David Hildenbrand (Arm) wrote: >> On 9/16/26 11:35, Breno Leitao wrote: >>> >>> hmmm, I am not sure I see it that way. >>> >>> The loop only runs for a block the bitmap marks. On a machine with nothing >>> recorded the bitmap is all zeros, the range_contains_poisoned_memory() check >>> right above it returns false, and the loop never executes. >>> >>> What every boot does pay is that check, once per block. The stub installs >>> the table whether or not anything was ever recorded in it, so this is not a >>> NULL test: it is two 64-bit divisions by the unit size plus a >>> find_next_bit() over the single word a 128M block covers at one bit per 2M. >>> >>> The real cost (that "for loop above"), comes when you kexec (not on cold >>> boot -- given the bitmap is empty), and you are trying to init >>> a memory block that has poisoned pages into it. Which seems the right >>> trade-off, no? >>> >>> That said, can we do better? Yes. The silly win is to let the table say >>> whether anything was ever recorded in it, something like a >>> linux_efi_poisoned_memory->empty that the first recorded frame clears, >>> and return on that before the bitmap is reached at all. >>> >>> Is this what you are looking for, or something more drastic? >> >> Ah, that magical "range_contains_poisoned_memory" does a bitmap scan? >> >> I'm sorry, but that is absolutely confusing. >> >> There is no way someone will figure out that range_contains_poisoned_memory() >> queries some efi specific bitmap that won't even be able to represent any memory >> outside of it's range. >> >> I don't really have time to give a better solution, but starting with the >> naming, range_contains_poisoned_memory() is just absolutely misleading. > > Fair point, I'll clean up the naming in the next revision. > > I'll also add that ->empty field, which should help locate this bit > faster and may let us skip the bitmap query entirely on the happy path. > > Anything else you'd like addressed? > > Good to know this moved the needle from "David hates this feature" to > "David only hates the naming" -- I'll take that as progress. :-P ;) I think the crucial part is to find a way to cleanly distinguish our source of information, and also how the source does only apply to some memory. Regarding this patch here, I'd assume it's sufficient. But I do wonder why we are walking pages when we have a bitmap to walk/process at hand? -- Cheers, David